Method of annealing sheet copper



Aug. 18, 1931. G. A. HEMPSTEAD 1,819,291

METHOD OF ANNEALING SHEET COPPER Filed Jan. 30, 1930 WITNESSES INVENTO RW d 3 W Q WQ w 1o yention is especially applicable to the heats sheetcopper as ust copper in muflle,

2 to heat sheet copper directly by i have considered it to be impossibleto so heat ity of the material by reason of the alloying Patented Aug.18, 1931 UNITED STATES PATENT OFFICE".

To run narrower. BRASS a or onto GEORGE A. HEMIPSTEAD, OF LISBON, OHIO,ASSIGNOB COPPER 00., OF LISBON, OHIO, A CORPORATION MEilTHOD OFANNEALIIVG SHEE'IP'COPPEB Application filed January 30, 1930. Serial No.424,567.

The invention relates to the heating of I The invention is predicatedupon my dissheet metal, andwhile in its broader aspects covery, madeafter extensive study and exit is unlimited to the heating of anyparticuerimentation, that sheet copper may be lar sheet metal, it hasbeen found to be espereadily heated at low fuel, labor and furnace ciallapplicable to the heating of sheet cop installation and up-keep costs,by impinging per, by which is meant throughout the speciupon the top andbottom of the sheet jet flames of raw fuel gas confined in a furnacechamber constructed to supply air for supporting combustion of the gas.I have further discovered that when sheet copper is annealed in themanner thus generally explained, and as will presently be described ingreater detail, the sheet is of superior quality, that there is aminimum loss of metal due to oxidation, and that the surface of thesheet is not injured. Specifically, sheet copper thus heated becomescoated with a film of black oxide after being removed from the furnace,which coating is much thinner than the oxide scale coatings formed onsuch sheet when heated according to the prevailing practice. This thinfilm of oxide may be readily removed without material loss of copper bypassing the sheet through a bath of sodium or potassium cyanide, orother suitable chemical. In the practice of the invention sheetcopfication, and in the claims, any copper base sheet materialcontaining not less than about 50% by weight of copper. Because'the in-.mg, either for working or for annealing, o defined, it is hereindescribed with reference to such applicability. The prevailing practiceis to heat sheet or semi-muffle furnaces, by the latter of which ismeant a furnace in which heating flames are prevented from directlyimpinging upon the sheet. Because such attempts as have heretofore beenmade flames have resulted in producing on the sheet what is generallydesignated as an orange skin surace, which is a roughness that cannot bere-' moved by pickling, those sldlled in the art this material. Also,because copper readily alloys with various elements, previous atper, andsheets of other metals or. alloys tempts toheat sheet copper'by'directflames WlllCh may be similarly treated, are heated,

either'for working or for annealing, by causing them to movecontinuously through an open-ended low-tunnel furnace in which the sheetis heated by direct contact with imping ing neutral jet flames ofnatural or artificial fuel gas which envelop the sheet and protect itagainst oxidation. The fuel gas is preferably supplied directly to thetunnel of the furnace without being previously mixed with air or anyother oxygen supply, the oxygen for supporting the combustion of the gasbeing supplied by air which enters the open ends of the tunnel.Preferably, the impinging flames of fuel gas are placed at each end ofthe tunnel, both above and below the sheet passing throu h it, and theproducts of combustion are withdrawn from the central portion of thetunnelso that the heating sheetimpinging and sheet-enveloping flamesflow from both ends of the tunnel towards its center.

The invention may have resulted in the impairment of the qualof thecopper with elements found in or mmgled with the products of combustion.Furthermore, in the prior heating of sheet copper in muflle orsemi-mufile furnaces, the procedure is slow, and the fuel, labor andfurnace up-keep costs .are .high. In' such furnaces the heating of thesheet copper is effected by radiation from the bottoms, sides and crownsof the heating chambers which must be first heated to a hightemperature, and which, on account of such high heating, readily spall,crumble and wear away. uch furnaces are also'objectionable becauseefiicient and proper operating conditions are diflicult to obtain andmaintain due to the human element entering into their operation, as wellas to openings in the furnace doors, and to unskillful firing and poorbalance of flames on account of the failure of mechanical fuel mixturesto function umformly.

be further explained with reference to the accompanying drawings whichsomewhat diagrammatically illustrate a simple form of apparatus withwhich it may be practiced. In the drawings, Fig. 1 is a longitudinalcentral sectional View of an annealing furnace, and Fig. 2 a transversesectional view-taken on the line II-II, Fig. 1.

In Fig. 1 there is shown a tunnel furnace comprising two like units, thenumber of which may be varied depending upon the clifferent requirementsof service. Each furnace comprises a 10v; tunnel 1 open at each end andprovided centrally with a flue 2 for of excess products of continuousconveyor 3 adapted to be moved at various suitable speeds, as by avariable speed electric motor 11. The sheets are moved from left toright through the furnace as viewed in Fig. 1, and emerge from thefurnace on an exposed extension of the conveyor. Raw fuel gas, eithernatural or artificial, is supplied to each end of each tunnel y burnerpipes 4, connected to a supply pipe 5, and arranged above and belowconveyor 3.

he arrangement of pipes 4, and the disposition of the burner openings inthem is such flames impinge directly upon and entirely envelop thesheets passing through furnace. The entire supply of oxygen orsupporting the combustion of the fuel gas is that of the air enteringthe open ends of the tunnel.

I have found that by properly controlling the supply of gas to productsof y properly regulating the rate of travel of continuous conveyor 3,sheet copper may be rapidly heated and annealed by their direct contactwith combusted fuel gas impinging flames which also protect the sheetagainst excessive oxidation. The copper, being a rapid conductor ofheat, absorbs for useful The heating or annealing being effected bydirect contact with the combusted impinging jet gas flames, the furnacemaybe of much eating types of furnace which are wasteful of fuel andexpensiveto construct and maintain. Different furnaces may beconstructed to heat or anneal diflerent sized sheets, thus making itunnecessary to operate large furnaces forvsmall sheets. These and otherad vantages of my invention have been well established by extensivecommercial prac tice.

1 By way of example, and not of limitation, I have found that a standardsheet of copper. 30 inches wide, 96 inches long and .0215 of y. of thetunnel.

for supporting combustion being an inch in thickness, may be fullyannealed by passing it at the rate of 42 feet per minute through adouble unit furnace of the form shown in the drawings,

copper sheet may be raised to its annealing temperature of about 1100 F.with a furnace temperature as low as 400 F. However, prolonged use ofthe furnace results in its temperature being increased materially abovethis amount. I have raised the temperature of copper sheet to about 1500F. without the formation of sufficient oxide on the sheet to cause it toscale. Over an extended period of time full annealing of this materialhas been effected in this furnace by an average consumption of 557 cubicfeet of natural gas per 1000 pounds of metal.

According to the provisions of the patent statutes, I have explained theprinciple and mode of construction and operation of my invention andhave described the preferred manner of practicing it, and haveillustrated apparatus whereby it may be practiced. However, I desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described andillustrated.

I claim as my invention:

1. The method of heating sheet copper, which consists of passing suchsheet continu-- ously throug an open ended tunnel furnace, and heatingthe sheet therein by'enveloping it in impinging jet flames of fuel gasto which 2. The method of heating sheet, copper,

which consists of passing such sheetcontinuously through an open endedtunnel furnace, and heating the sheet therein by enveloping it inimpinging jet flames offuel gas applied at each end of the tunnel, theoxygen for supporting combustion of thefuel gas eing supplied by airentering the open ends combustion fromthe central portion of the tunnel.

end of the tunnel, the oxygen of the fuel gas supplied solel open endsof the tunnel, and removing the products of combustion from the centralportion of the tunnel.

In testimony whereof, I.

GEORGE A.

sign my name.

HEMPSTEAD.

and removing the products of r y by air entering the l

